The invention relates to telecommunications technology and especially to the mechanisms that support group communication.
In mobile telephone networks used by fire and rescue authorities and the police or companies, group communication between authorities performing official tasks is among the most essential telecommunications traffic in the network. Such networks are often called private or professional mobile radio (PMR) networks.
TETRA (TErrestrial Trunked RAdio) is a standard for digital PMR systems defined by ETSI (European Telecommunications Standards Institute). Group communication can, in turn, be defined as traffic, in which a call or some other data transmission or telecommunications action can be established simultaneously for a predefined user group.
Usually group traffic is implemented as ‘push-to-talk, release-to-listen’ traffic, in which a radio channel is reserved while the push-to-talk switch is pressed and possibly for a time after the switch is released, i.e. a guard period.
In a prior-art group call management mechanism, a centralized control centre to which all speech item requests are transmitted is appointed for the group. The control centre maintains a speech item queue and reserves resources from other centres defined as belonging to the area of the group. Advanced centralized control centres are also able to keep track of the locations of the members of a group in the area of the group and to reserve resources from the base stations where the group members are located at a specific moment.
In fault situations of a communication network, a situation may arise in which group call management from a centralized point is not possible and group calls are prevented at least partly. This may be due to an earthquake or sabotage that has damaged the centre in the centralized point.
In fault situations of a communication network as well as in catastrophes, it is essential that group traffic between authorities performing the same task be secured.